Seismic performance of steel X-knee-braced frames equipped with shape memory alloy bars

The utilization of smart materials in construction, to improve the seismic response of structures is one of the most interesting topics in earthquake engineering. Accordingly, this study aims to investigate the use of shape memory alloy (SMA) bars within X-knee-braced frames (X-KBFs). To fulfill the objectives of this research, three 3-, 5-, and 7-story frames are modeled in the OpenSees at first. Then, by placing these superelastic elements between the beam-column joints and knee members, some structural properties such as stiffness, ductility, strength, and recentering are examined against seismic loading. Moreover, by performing pushover analyses, the influence of SMA bars on the formation of plastic hinges is investigated. Considering 12 different diameters for SMA bars, a number of nonlinear time-history analyses are performed in the software framework of OpenSees; and, the results show that the employment of such members does not remarkably change the stiffness, ductility, and strength of structures. Contrary to these features, an interesting finding is that the permanent roof displacements of the structures are significantly reduced through these elements due to their excellent recentering capacity.